The present invention relates to a blower fan suitable for use in blowing apparatuses such as haircombs, forced air circulation devices, multi-purpose blowing apparatuses for use in the agricultural field and the like.
The present invention also relates to a blowing apparatus, comprising an engine, a blower fan moved by the engine and adapted to generate a radial air flow, a volute header enclosing said blower fan and adapted to convey said radial flow at least partly towards use means.
It is known that in many applications, such as in the agricultural field, when cleaning of streets and pavements or grasslands is concerned, as well as for other similar application fields, portable blowing apparatus are used which are adapted to produce a strong air jet.
This air jet can be employed for spraying or atomizing anticryptogamic or manuring liquids held in small tanks associated with the blowing apparatus itself, or may constitute an air current of appropriate force for removal and displacement of leaves or other light material from road surfaces or grasslands.
The blowing apparatus generally comprises a two-stroke inner combustion engine moving a centrifugal blower fan adapted to generate a substantially radial delivery air flow. The blower fan is externally surrounded by a volute header adapted to convey the air flow at least partly towards the intended use means, which may consist for example of a flexible hose adapted to be gripped by an operator responsible for the apparatus.
In the known art, the blower fans bear a number of blades which, during suction, generate a single axial air flow converging towards the blades themselves, on the opposite side with respect to the engine.
Part of the delivery air flow is deviated from the provided main use and conveyed towards the engine sometimes contained at least partly in a casing, for cooling of the engine itself.
The known art briefly described above has some important drawbacks.
In fact, first of all, it is characterized by a non-optimal yield because the delivery air flow is not completely conveyed towards the use means provided for the blowing apparatus, but it is partly deviated for engine cooling. Part of the used energy is therefore employed for merely achieving a correct engine operation and the air flow really utilized has a smaller flow rate than that emitted from the wheel fan.
It should be also pointed out that engine cooling by means of an overpressure air flow is often of poor efficiency; in fact, due to flow resistance to which the air flow is submitted while passing through often tortuous passageways between the engine and casing, overpressure is reduced or eliminated, which will therefore stop or at all events decrease the air outflow. It is to be added that if the engine is not provided with a casing for improving cooling thereof, it produces a strong noise often higher than the limits that in some countries are allowed by regulations against sound pollution.
At all events, the blowing apparatus in accordance with the known art, even if it is provided with an engine-holding casing, often does not succeed in maintaining the engine noise within limits of acceptability because the cooling air flow, after impinging on the engine, flows out of the casing together with sound waves.
It is also to be noted that the air flow dedicated to engine cooling, heated by heat exchange with said engine, forms a troublesome hot air mass often directed towards the operator or other people near him/her.
Apart from what just stated for the known blowing apparatuses, it should also be pointed out that known types of blower fans are subject to important drawbacks.
In fact, it should be firstly recognized that the blower fans having a single axial-suction flow are asymmetric from a mechanical and hydraulic point of view; therefore they can be easily submitted to vibrations, giving rise to a further noise source.
Beside this, it is to be noted that the known architectures of blower fans are not optimized in terms of noise reduction (which is substantially generated by extensive turbulent flow phenomena throughout the volume existing between the blades).
At the same time, the traditional blower fans are designed to ensure a very precisely established air flow, which is taken from a predetermined suction port (having a correspondent passage area). If such passage area is partially choked, for example by dirt or solid bodies such leafs, papers or whatever else, the known blower fans"" efficiency is strongly affected, and consequently the air flow produced by the same blower fans decreases dramatically.
Under this situation, the technical task underlying the present invention is to conceive a multi-purpose blowing apparatus capable of substantially obviating the mentioned drawbacks.
Within the scope of this technical task, it is an important object of the invention to devise a blowing apparatus having a high yield and operating efficiency.
Another important object of the invention is to devise a blowing apparatus capable of improving efficiency in cooling the engine provided therein.
A further object is to provide a blowing apparatus emitting a reduced level of noise to the surrounding atmosphere.
A still further object of the invention is to devise a blowing apparatus capable of exclusively producing an air current to the outside, the direction of which is directly controlled by the operator without generating any troublesome hot air current directed against the operator or other people.
In the spirit of the present invention, another significant technical task consists in providing for a blower fan which is capable of greatly reducing the noise production, and at the same time which is capable of providing a great aerodynamic efficiency.
More in detail, the present invention aims at achieving a blower fan which may grant a high air flow rate in various operative conditions, even despite of a partial clogging of suction ports of the apparatus wherein the blower fan is operating.
Finally, the present invention is devoted to provide a blower fan which presents a well-balanced structure and which is easy to assemble, thus bringing advantages in reliability and productive economy.
The technical task mentioned and the objects specified are substantially achieved by a blower fan (and a blowing apparatus provided of such a blower fan) having the structural features retrievable in the alleged claims.